This invention relates to a corotating preventor in a ground improvement apparatus for performing the agitation mixing of the ground efficiently in the ground improvement wherein soils and fillers are mechanically mixed to solidify cylindrically.
A conventional soil improvement apparatus comprises a excavation rod provided with an excavation blade at the tip end thereof and plural steps of agitation blades at the upper portions thereof, said excavation rod being allowed to excavate the soil rotatively by means of an excavating mechanism and performing the solidification of the soil by fillers such as sodium silicate or cement milk fed from a liquid passage provided within the excavation rod with reinforced agitation at low pressure at the time of the excavation or of the drawing out of the rod.
However, although such kind of soil improvement apparatus is effective to the soil such as sand soil or silt since the soil is once cut by a mixing head and the fillers are fed to the clearance between the cut soils at low pressure to mix and agitate the fillers with excavated soils, in case of a clay, particularly in a hard clay or a peat layer, the soil to be improved tends to be corotated with the agitation blades which makes it impossible to mix and agitate both cut soils and fillers effectively. As a means to solve this problem, there exist patent laid open No. 58(1983)-29374 and patent laid open No. 58(1983)-29375 developed by the same Applicants. The former technique is, as shown in FIG. 6, a mixing agitation blade apparatus for cut soils characterized in that corotating preventors 4 are positioned between an excavation blade 2 of an excavation rod 1 and an agitation blade 3 and/or between the respective agitation blades 3, the corotation preventing blade 6 having a larger diameter than the excavation diameter of the above excavation blade 2 rotatively to the excavation rod 1 by means of boss 5.
The latter patent discloses a mixing agitation blade apparatus for cut soils characterized in that a corotating prevent-or which comprises a cylindrical body having an approximately equal diameter to the excavation diameter is positioned above an excavation blade of the excavation rod, and is rotatively attached to said rod by means of a boss and arm. A resistant plate projects outwardly from the periphery of the corotating preventor body and a corotating prevention blade is extended inwardly on from the cylindrical body.
However, in the above apparatus the distance between the excavation blade 2 and the corotating prevention blade 6 may not be small enough to prevent the soil between the lower end of the corotating prevention blade 6 and of the excavation blade 2 may still adhere to the excavation blade 2 which causes the corotation. This trend is particularly evident in a ground having a very strong adhesion such as hard clay and the like.